Stent-graft securement device

ABSTRACT

A stent attachment and deployment mechanism is utilized to prevent the distal end of an endoprosthesis comprising fixation barbs or other fixation mechanism from deploying prior to the remaining sections of the fixation device. With this stent attachment and deployment mechanism accurate deployment may be achieved.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to aneurismal repair devices, and moreparticularly, to devices for restraining the cranial end of anendoprosthesis of an aneurismal repair device until the remainingportion of the endoprosthesis is deployed and fully expanded and thendeploying the cranial end.

2. Discussion of the Related Art

An aneurysm is an abnormal dilation of a layer or layers of an arterialwall, usually caused by a systemic collagen synthetic or structuraldefect. An abdominal aortic aneurysm is an aneurysm in the abdominalportion of the aorta, usually located in or near one or both of the twoiliac arteries or near the renal arteries. The aneurysm often arises inthe infrarenal portion of the diseased aorta, for example, below thekidneys. A thoracic aortic aneurysm is an aneurysm in the thoracicportion of the aorta. When left untreated, the aneurysm may rupture,usually causing rapid fatal hemorrhaging.

Aneurysms may be classified or typed by their position as well as by thenumber of aneurysms in a cluster. Typically, abdominal aortic aneurysmsmay be classified into five types. A Type I aneurysm is a singledilation located between the renal arteries and the iliac arteries.Typically, in a Type I aneurysm, the aorta is healthy between the renalarteries and the aneurysm and between the aneurysm and the iliacarteries.

A Type II A aneurysm is a single dilation located between the renalarteries and the iliac arteries. In a Type II A aneurysm, the aorta ishealthy between the renal arteries and the aneurysm, but not healthybetween the aneurysm and the iliac arteries. In other words, thedilation extends to the aortic bifurcation. A Type II B aneurysmcomprises three dilations. One dilation is located between the renalarteries and the iliac arteries. Like a Type II A aneurysm, the aorta ishealthy between the aneurysm and the renal arteries, but not healthybetween the aneurysm and the iliac arteries. The other two dilations arelocated in the iliac arteries between the aortic bifurcation and thebifurcations between the external iliacs and the internal iliacs. Theiliac arteries are healthy between the iliac bifurcation and theaneurysms. A Type II C aneurysm also comprises three dilations. However,in a Type II C aneurysm, the dilations in the iliac arteries extend tothe iliac bifurcation.

A Type III aneurysm is a single dilation located between the renalarteries and the iliac arteries. In a Type III aneurysm, the aorta isnot healthy between the renal arteries and the aneurysm. In other words,the dilation extends to the renal arteries.

A ruptured abdominal aortic aneurysm is presently the thirteenth leadingcause of death in the United States. The routine management of abdominalaortic aneurysms has been surgical bypass, with the placement of a graftin the involved or dilated segment. Although resection with a syntheticgraft via a transperitoneal or retroperitoneal procedure has been thestandard treatment, it is associated with significant risk. For example,complications include perioperative myocardial ischemia, renal failure,erectile impotence, intestinal ischemia, infection, lower limb ischemia,spinal cord injury with paralysis, aorta-enteric fistula, and death.Surgical treatment of abdominal aortic aneurysms is associated with anoverall mortality rate of five percent in asymptomatic patients, sixteento nineteen percent in symptomatic patients, and is as high as fiftypercent in patients with ruptured abdominal aortic aneurysms.

Disadvantages associated with conventional surgery, in addition to thehigh mortality rate, include an extended recovery period associated withthe large surgical incision and the opening of the abdominal cavity,difficulties in suturing the graft to the aorta, the loss of theexisting thrombosis to support and reinforce the graft, theunsuitability of the surgery for many patients having abdominal aorticaneurysms, and the problems associated with performing the surgery on anemergency basis after the aneurysm has ruptured. Further, the typicalrecovery period is from one to two weeks in the hospital and aconvalescence period, at home, ranging from two to three months or more,if complications ensue. Since many patients having abdominal aorticaneurysms have other chronic illnesses, such as heart, lung, liverand/or kidney disease, coupled with the fact that many of these patientsare older, they are less than ideal candidates for surgery.

The occurrence of aneurysms is not confined to the abdominal region.While abdominal aortic aneurysms are generally the most common,aneurysms in other regions of the aorta or one of its branches arepossible. For example, aneurysms may occur in the thoracic aorta. As isthe case with abdominal aortic aneurysms, the widely accepted approachto treating an aneurysm in the thoracic aorta is surgical repair,involving replacing the aneurysmal segment with a prosthetic device.This surgery, as described above, is a major undertaking, withassociated high risks and with significant mortality and morbidity.

Over the past five years, there has been a great deal of researchdirected at developing less invasive, endovascular, i.e., catheterdirected, techniques for the treatment of aneurysms, specificallyabdominal aortic aneurysms. This has been facilitated by the developmentof vascular stents, which can and have been used in conjunction withstandard or thin-wall graft material in order to create a stent-graft orendograft. The potential advantages of less invasive treatments haveincluded reduced surgical morbidity and mortality along with shorterhospital and intensive care unit stays.

Stent-grafts or endoprostheses are now Food and Drug Administration(FDA) approved and commercially available. Their delivery proceduretypically involves advanced angiographic techniques performed throughvascular accesses gained via surgical cut down of a remote artery, whichmay include the common femoral or brachial arteries. Over a guidewire,the appropriate size introducer will be placed. The catheter andguidewire are passed through the aneurysm. Through the introducer, thestent-graft will be advanced to the appropriate position. Typicaldeployment of the stent-graft device requires withdrawal of an outersheath while maintaining the position of the stent-graft with aninner-stabilizing device. Most stent-grafts are self-expanding; however,an additional angioplasty procedure, e.g., balloon angioplasty, may berequired to secure the position of the stent-graft. Following theplacement of the stent-graft, standard angiographic views may beobtained.

Due to the large diameter of the above-described devices, typicallygreater than twenty French (3F=1 mm), arteriotomy closure typicallyrequires open surgical repair. Some procedures may require additionalsurgical techniques, such as hypogastric artery embolization, vesselligation, or surgical bypass in order to adequately treat the aneurysmor to maintain blood flow to both lower extremities. Likewise, someprocedures will require additional advanced catheter directedtechniques, such as angioplasty, stent placement and embolization, inorder to successfully exclude the aneurysm and efficiently manage leaks.

While the above-described endoprostheses represent a significantimprovement over conventional surgical techniques, there is a need toimprove the endoprostheses, their method of use and their applicabilityto varied biological conditions. Accordingly, in order to provide a safeand effective alternate means for treating aneurysms, includingabdominal aortic aneurysms and thoracic aortic aneurysms, a number ofdifficulties associated with currently known endoprostheses and theirdelivery systems must be overcome. One concern with the use ofendoprostheses is the prevention of endo-leaks and the disruption of thenormal fluid dynamics of the vasculature. Devices using any technologyshould preferably be simple to position and reposition as necessary,should preferably provide an acute, fluid tight seal, and shouldpreferably be anchored to prevent migration without interfering withnormal blood flow in both the aneurysmal vessel as well as branchingvessels. In addition, devices using the technology should preferably beable to be anchored, sealed, and maintained in bifurcated vessels,tortuous vessels, highly angulated vessels, partially diseased vessels,calcified vessels, odd shaped vessels, short vessels, and long vessels.In order to accomplish this, the endoprostheses should preferably behighly durable, extendable and re-configurable while maintaining acuteand long-term fluid tight seals and anchoring positions.

The endoprostheses should also preferably be able to be deliveredpercutaneously utilizing catheters, guidewires and other devices whichsubstantially eliminate the need for open surgical intervention.Accordingly, the diameter of the endoprostheses in the catheter is animportant factor. This is especially true for aneurysms in the largervessels, such as the thoracic aorta. In addition, the endoprosthesesshould preferably be percutaneously delivered and deployed such thatsurgical cut down is unnecessary.

During deployment of a typical device, the endoprosthesis is heldstationary while an outer catheter sheath is retracted and theendoprosthesis expands into position due to the self-expandingproperties of the underlying stent structure. Due to the potentialtortuous nature of the human anatomy, the delivery catheter containingthe endoprosthesis generally lies up against one side of the vesselprior to deployment. It has been observed in testing that when a suprarenal stent with barbs is the first portion of the endoprosthesis toexpand, the barbs closest to the vessel wall may make premature contactwith the wall before the stent has had a chance to fully expand. Thiscreates a situation where the portion of the stent farthest away fromthe wall during expansion actually accounts for a disproportionateamount of the expansion of the stent in order for the entire stent tomeet the internal diameter of the vessel. The sections of the stent thatare up against the wall do not fully expand and the stent will notachieve full opposition against the vessel wall. Accordingly, it wouldbe highly advantageous to have a device that delays the opening of thecranial end until the remaining portions are deployed.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages associated withcurrently utilized aneurismal repair devices and their associateddeployment mechanisms.

In accordance with a first aspect, the present invention is directed toa stent-graft securement device for a catheter based stent-graftdelivery system. The stent-graft securement device comprising a holdingdevice which is integral with the catheter based stent-graft deliverysystem, the holding device including a wire holder slidably engaged toan inner member of the catheter based stent-graft delivery system,engagement wires, a wire guide fixedly mounted to the inner member ofthe catheter based stent-graft delivery system distal to the wireholder, and a distal receiver fixedly mounted to the inner member of thecatheter based stent-graft delivery system distal from the wire guide,and eyelets integral with a stent-graft and extending from the endthereof, the engagement wires originating from the wire holder, passingthrough the wire guide, the eyelets and into distal receiver, the wireholder being configured to move proximally, thereby retracting theengagement wires from the distal receiver and eyelets and into the wireguide.

The present invention is directed to a stent-graft securement mechanism,in which both the stent-graft and the delivery device or deliverycatheter are modified. Essentially, the stent-graft securement mechanismcomprises a holding device which is integral with the delivery catheterand an eyelet configuration integral with the distal end of thestent-graft. Each of these components is designed to mate and work withthe other in order to achieve the desired functions; namely, to overcomethe drawbacks associated with currently utilized stent-graft deliverysystems as briefly described above.

The holding device comprises four basic components; namely, the wireholder, the engagement wires, the wire guide and the distal receiver.These four components are integral with the delivery system and functionto release the distal end of the stent-graft via action of thephysician. The eyelet configuration is an additional element of thestent-graft. The engagement wires simply run from the wire holder,through the wire guide, through the eyelets and into the distalreceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the invention will beapparent from the following, more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

FIG. 1 is a diagrammatic representation of the exemplary anchoring andsealing prosthesis in accordance with the present invention.

FIG. 2 is a diagrammatic representation of an exemplary anchoring andsealing prosthesis with no graft material and/or stitching in certainlocations in accordance with the present invention.

FIG. 3 is an elevational view of an endovascular graft in accordancewith the present invention.

FIG. 4 is a perspective view of an expanded stent segment of theendovascular graft in accordance with the present invention.

FIG. 4A is a fragmentary perspective view of a portion of the stentsegment of FIG. 4.

FIG. 4B is a fragmentary perspective view of a portion of the stentsegment of FIG. 4.

FIG. 4C is an enlarged plan view of a section of the stent segment ofFIG. 4.

FIG. 4D is an enlarged plan view of a section of the stent segment ofFIG. 4.

FIG. 5 is a perspective view of another expanded stent segment of theendovascular graft in accordance with the present invention.

FIG. 6 is an elevational view of an endovascular graft in accordancewith the present invention.

FIG. 7 is a first diagrammatic representation of a portion stent-graftsecurement device in accordance with the present invention.

FIG. 8 is a second diagrammatic representation of a portion stent-graftsecurement device in accordance with the present invention.

FIG. 9 is a third diagrammatic representation of a portion stent-graftsecurement device in accordance with the present invention.

FIG. 10 is a fourth diagrammatic representation of a portion stent-graftsecurement device in accordance with the present invention.

FIG. 11 is a fifth diagrammatic representation of a portion stent-graftsecurement device in accordance with the present invention.

FIG. 12 is a sixth diagrammatic representation of a portion stent-graftsecurement device in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is illustrated an exemplary embodiment of ananchoring and sealing component 100 of an aneurysm repair system. Theanchoring and sealing component 100 comprises a trunk section 102 and abifurcated section, including two legs 104, 106. Graft material 108,described in detail below, is affixed to at least a portion of the trunksection 102 and to all of the legs 104, 106. The graft material may beattached via any number of means. In the exemplary embodiment, the graftmaterial 108 is attached to various portions of the underlying structureby sutures 110. As illustrated, the graft material 108 is affixed with acontinuous stitch pattern on the end of the trunk section 102 and bysingle stitches elsewhere. It is important to note that any stitchpattern may be utilized, and other devices, such as staples, may beutilized to connect the graft material 108 to the underlying structure.The sutures 110 may comprise any suitable biocompatible material that ispreferably highly durable and wear resistant.

The underlying structure of the trunk section 102, as illustrated inFIG. 2, comprises a substantially tubular stent structure or latticecomprising multiple stent sections. The stent or lattice structurecomprises a single row of substantially diamond shaped elements 112 onone end, multiple rows of substantially diamond shaped elements 114 onthe other end, a plurality of longitudinal struts 116 and a single,substantially zigzag shaped stent element 117. The plurality oflongitudinal struts 116 are connected to the apexes of the substantiallydiamond shaped elements 114. The single, substantially zigzag shapedstent element 117 comprises a number of barbs 119 protruding therefromfor anchoring the device in the vessel to be repaired. This exemplaryembodiment may be utilized for anchoring and sealing in positionswherein there are branches off the main artery. For example, thisexemplary embodiment may be utilized for supra-renal anchoring.Accordingly, the graft material 108 is only attached below thelongitudinal struts 116 so that blood may flow into the renal arteriesfrom the aorta. Infra-renal designs are also possible.

The underlying structure of the bifurcated section, as illustrated inFIG. 2, comprises a plurality of individual, substantially tubular stentelements 118. Each stent element 118 comprises a substantially zigzagpattern. As illustrated, leg 104 comprises three stent elements 118 a,118 b, 118 c and leg 106 comprises two stent elements 118 d, 118 e. Asillustrated, in this exemplary embodiment, the stent elements do notline up and the legs are of two different lengths. This exemplary designallows for nesting of the legs 104, 106 such that the profile of thedevice is reduced.

In order to compensate for the missing stent elements, the legs areconnected at the bifurcation as illustrated in FIG. 1. The legs 104, 106may be connected in any suitable manner. In the exemplary embodiment,the two legs 104, 106 are connected by suturing them together. Thesutures 120 connect the graft material 108 on each leg 104, 106together. The sutures may be non-biodegradable or biodegradable.Biodegradable sutures would dissolve over time thereby allowing the twolegs to move independently.

Referring now to FIG. 3, there is illustrated an exemplary embodiment ofan endovascular graft 300 of an aneurysm repair system. The exemplaryendovascular graft 300 comprises one or more first stent segments 310,one second stent segment 320 and a third stent segment 330. In a typicaluse scenario, the third stent segment 330 would be anchored in healthytissue below the aneurysm and the uppermost first stent segment 310would be in fluid communication with the anchoring and sealing component100. The second stent segment 320 comprises a tapered profile, having adiameter at one end equal to that of the first stent segment 310 and adiameter at the other end equal to that of the third stent segment 330.The length of the endovascular graft 300 may be adjusted by varying thenumber of first stent segments 310 utilized.

FIG. 4 is a detailed perspective view of an exemplary embodiment of thethird stent segment 330. The third stent segment 330 comprises aplurality of struts 332 connected in a substantially zigzag pattern. Asillustrated, the exemplary third stent segment 330 comprises three setsof zigzag-connected struts 332, thereby forming substantiallydiamond-shaped cells. The non-connected apex 334 of each diamond shapedcell, illustrated in greater detail in FIG. 4A, comprises a smooth,uniform width curved region formed at the intersection of two struts 332of each diamond-shaped cell. This shape is cut directly into the stentsegment 330 during the initial machining steps, typically laser cutting,and is maintained during all subsequent finishing processing. Thejunctions 336 between the zigzag-connected struts 332, illustrated ingreater detail in FIG. 4B occurs at the intersection of four struts 332.Preferably, each junction 336 of four struts 332 comprises twoindentations 338 and 340 as illustrated in FIG. 4B.

The regions proximate the non-connected apexes 334 and the junctions 336are generally the highest stress regions in the third stent segment 330.To minimize the stresses in these regions, these regions are designed tomaintain uniform beam widths proximate where the struts 332interconnect. Beam width refers to the width of a strut junction 336.Indentations 338 and 340 are cut or machined into the junctions 336 tomaintain a uniform beam width in this area, which is generally subjectto the highest stress. Essentially, by designing the junctions 336 tomaintain uniform beam widths, the stress and strain that would normallybuild up in a concentrated area, proximate the junction 336, is allowedto spread out into the connecting regions, thereby lowering the peakvalues of the stress and strain in the stent structure.

To further minimize the maximum stresses in the struts 332 of the thirdstent segment 330, the struts 332 may have a tapering width. Forexample, in one exemplary embodiment, the struts 332 may be designed tobecome wider as it approaches a junction 336. FIG. 4C is an enlargedpartial view of the third sent segment 330 in its expanded conditionswhich illustrates the tapering width of the struts 332. In thisexemplary embodiment, the strut 332 proximate the junction 336 (width a)is about 0.025 cm and gradually tapers to a dimension of about 0.0178 cmin the mid-region of the strut 332 (width b). By tapering the struts'widths, the stresses in the struts 332 adjacent the junction 336 isspread out away from the junction 336. The tapering of the struts 332 isaccomplished during the machining of the tube of material from which thestent 330 is cut. However, by tapering the struts 332 in this manner,there is a tradeoff. The stent segment 330 becomes somewhat lessresistant to localized deformations, caused for example, by a protrusionwithin the vessel lumen. This localized deformation may lead to a localtorsional loading on some of the struts 332, and, therefore, since thestruts 332 in this exemplary embodiment have a relatively significantportion of their length with a reduced width, their torsional rigidityis reduced.

If maximizing the resistance to localized deformation is preferred, thestruts 332 may be maintained at a uniform width, or more preferably havea reverse taper, as illustrated in FIG. 4D, wherein the width at point ais less than the width at point b. In this exemplary embodiment, thereverse taper struts 332 are about 0.025 cm proximate the junction 336and about 0.028 cm in the central region of the struts. While thisreverse taper tends to increase the stresses somewhat proximate thejunctions 336, this increase is very small relative to the decrease instresses gained by having the side indentations 338, 340 illustrated inFIG. 4B, as well as the uniform width connections illustrated in FIG.4A. In addition, since the reverse taper serves to increase thetorsional rigidity of the strut 332, the stent structure resists localdeformation and tends to maintain a substantially circularcross-sectional geometry, even if the lumen into which the stent ispositioned in non-circular in cross-section.

In a preferred exemplary embodiment, the third stent segment 330 isfabricated from a laser cut tube, of initial dimensions 0.229 cm insidediameter by 0.318 cm outside diameter. The struts 332 are preferably0.0229 cm wide adjacent the four strut junctions 336 and six mm long,with a reverse taper strut width. Also, to minimize the number ofdifferent diameter combination of grafts systems, it is preferred thatthe third stent segment 330 have an expanded diameter of sixteen mm.Similarly, the proximal portion of the graft material forming the legsis flared, having a diameter of sixteen mm. This single diameter for thethird stent segment of the graft system would enable its use in arterieshaving a non-aneurysmal region of a diameter from between eight andfourteen mm in diameter. It is also contemplated that multiple diametercombinations of third stent segment 330 and graft flare would bedesirable.

Referring back to FIG. 3, the one or more first stent segments 310 arealso formed from a shape set laser cut tube, similar to the third stentsegment 330 described above. The one or more first stent segments 310comprise a single circumferential row of zigzag or sinusoidally arrangedelements. In the exemplary embodiment illustrated in FIG. 3, and ingreater detail in FIG. 5, the first stent segment 310 comprises tenzigzag or sinusoidal undulations. The one or more first stent segments310 are formed with uniform width connections at the intersections 314of the struts 312 forming the zigzag or sinusoidal pattern. The one ormore first stent segments 310 are preferably cut from tubing having aninside diameter of 0.251 cm and an outside diameter of 0.317 cm. Thestrut widths are preferably about 0.33 cm wide adjacent strutintersections 314 and the struts 312 are preferably seven mm long andthe one or more first stent segments 310 are preferably eleven mm indiameter when expanded.

The second stent segment 320 comprises a tapered profile, having adiameter at one end which is the same as the one or more first stentsegments 310, and a diameter at the other end matching the diameter ofthe third stent segment 330. The second stent segment 320 is identicalto the one or more first stent segments 310 except for the taper.

As is explained in detail subsequently, the stent segments 310, 320 and330 are secured in position by the graft material.

Nitinol is utilized in a wide variety of applications, including medicaldevice applications as described herein. Nitinol or Ni—Ti alloys arewidely utilized in the fabrication or construction of medical devicesfor a number of reasons, including its biomechanical compatibility, itsbiocompatibility, its fatigue resistance, its kink resistance, itsuniform plastic deformation, its magnetic resonance imagingcompatibility, its constant and gentle outward pressure, its dynamicinterference, its thermal deployment capability, its elastic deploymentcapability, its hysteresis characteristics and because it is modestlyradiopaque.

Nitinol, as described above, exhibits shape memory and/or superelasticcharacteristics. Shape memory characteristics may be simplisticallydescribed as follows. A metallic structure, for example a Nitinol tubethat is in an Austenite phase may be cooled to a temperature such thatit is in the Martensite phase. Once in the Martensite, the Nitinol tubemay be deformed into a particular configuration or shape by theapplication of stress. As long as the Nitinol tube is maintained in theMartensite phase, the Nitinol tube will remain in its deformed shape. Ifthe Nitinol tube is heated to a temperature sufficient to cause theNitinol tube to reach the Austenite phase, the Nitinol tube will returnto its original or programmed shape. The original shape is programmed tobe a particular shape by well known techniques. Superelasticcharacteristics may be simplistically described as follows. A metallicstructure, for example, a Nitinol tube that is in an Austenite phase maybe deformed to a particular shape or configuration by the application ofmechanical energy. The application of mechanical energy causes a stressinduced Martensite phase transformation. In other words, the mechanicalenergy causes the Nitinol tube to transform from the Austenite phase tothe Martensite phase. By utilizing the appropriate measuringinstruments, one can determine that the stress from the mechanicalenergy causes a temperature drop in the Nitinol tube. Once themechanical energy or stress is released, the Nitinol tube undergoesanother mechanical phase transformation back to the Austenite phase andthus its original or programmed shape. As described above, the originalshape is programmed by well known techniques. The Martensite andAustenite phases are common phases in many metals.

Medical devices constructed from Nitinol are typically utilized in boththe Martensite phase and/or the Austenite phase. The Martensite phase isthe low temperature phase. A material in the Martensite phase istypically very soft and malleable. These properties make it easier toshape or configure the Nitinol into complicated or complex structures.The Austenite phase is the high temperature phase. A material in theAustenite phase is generally much stronger than the material in theMartensite phase. Typically, many medical devices are cooled to theMartensite phase for manipulation and loading into delivery systems, asdescribed above with respect to stents and then when the device isdeployed at body temperature, they return to the Austenite phase.

The first, second and third stent segments 310, 320, 330 are preferablyself-expandable and formed from a shape memory alloy. Such an alloy maybe deformed from an original, heat-stable configuration to a second,heat-unstable configuration. The application of a desired temperaturecauses the alloy to revert to an original heat-stable configuration. Aparticularly preferred shape memory alloy for this application is binarynickel titanium alloy comprising about 55.8 percent Ni by weight,commercially available under the trade designation NITINOL. This NiTialloy undergoes a phase transformation at physiological temperatures. Astent made of this material is deformable when chilled. Thus, at lowtemperatures, for example, below twenty degrees centigrade, the stent iscompressed so that it can be delivered to the desired location. Thestent may be kept at low temperatures by circulating chilled salinesolutions. The stent expands when the chilled saline is removed and itis exposed to higher temperatures within the patient's body, generallyaround thirty-seven degrees centigrade.

In preferred embodiments, each stent is fabricated from a single pieceof alloy tubing. The tubing is laser cut, shape-set by placing thetubing on a mandrel, and heat-set to its desired expanded shape andsize.

In preferred embodiments, the shape setting is performed in stages atfive hundred degrees centigrade. That is, the stents are placed onsequentially larger mandrels and briefly heated to five hundred degreescentigrade. To minimize grain growth, the total time of exposure to atemperature of five hundred degrees centigrade is limited to fiveminutes. The stents are given their final shape set for four minutes atfive hundred fifty degrees centigrade, and then aged to a temperature offour hundred seventy degrees centigrade to import the proper martensiteto austenite transformation temperature, then blasted, as described indetail subsequently, before electropolishing. This heat treatmentprocess provides for a stent that has a martensite to austenitetransformation which occurs over a relatively narrow temperature range;for example, around fifteen degrees centigrade.

To improve the mechanical integrity of the stent, the rough edges leftby the laser cutting are removed by combination of mechanical gritblasting and electropolishing. The grit blasting is performed to removethe brittle recast layer left by the laser cutting process. This layeris not readily removable by the electropolishing process, and if leftintact, could lead to a brittle fracture of the stent struts. A solutionof seventy percent methanol and thirty percent nitric acid at atemperature of minus forty degrees centigrade or less has been shown towork effectively as an electropolishing solution. Electrical parametersof the electropolishing are selected to remove approximately 0.00127 cmof material from the surfaces of the struts. The clean, electropolishedsurface is the final desired surface for attachment to the graftmaterials. This surface has been found to import good corrosionresistance, fatigue resistance, and wear resistance.

The graft material or component 600, as illustrated in FIG. 6, may bemade from any number of suitable biocompatible materials, includingwoven, knitted, sutured, extruded, or cast materials comprisingpolyester, polytetrafluoroethylene, silicones, urethanes, and ultralightweight polyethylene, such as that commercially available under the tradedesignation SPECTRA™. The materials may be porous or nonporous.Exemplary materials include a woven polyester fabric made from DACRON™or other suitable PET-type polymers.

In one exemplary embodiment, the fabric for the graft material is aforty denier (denier is defined in grams of nine thousand meters of afilament or yarn), twenty-seven filament polyester yarn, having aboutseventy to one-hundred end yarns per cm per face and thirty-two toforty-six pick yarns per cm face. At this weave density, the graftmaterial is relatively impermeable to blood flow through the wall, butis relatively thin, ranging between 0.08 and 0.12 mm in wall thickness.

The graft component 600 is a single lumen tube and preferably has ataper and flared portion woven directly from the loom, as illustratedfor the endovascular graft 300 shown in FIG. 3.

Prior to attachment of the graft component 600 to the stents 310, 320,330, crimps are formed between the stent positions by placing the graftmaterial on a shaped mandrel and thermally forming indentations in thesurface. In the exemplary embodiment illustrated in FIGS. 3 and 6, thecrimps 602 in the graft 400 are about two mm long and 0.5 mm deep. Withthese dimensions, the endovascular graft 300 can bend and flex whilemaintaining an open lumen. Also, prior to attachment of the graftcomponent 600 to the stents 310, 320 330, the graft material is cut in ashape to mate with the end of each end stent.

As stated above, each of the stent segments 310, 320 and 330 is attachedto the graft material 600. The graft material 600 may be attached to thestent segments 310, 320, 330 in any number of suitable ways. In oneexemplary embodiment, the graft material 600 may be attached to thestent segments 310, 320, 330 by sutures.

The method of suturing stents in place is important for minimizing therelative motion or rubbing between the stent struts and the graftmaterial. Because of the pulsatile motion of the vasculature andtherefore the graft system, it is possible for relative motion to occur,particularly in areas where the graft system is in a bend, or if thereare residual folds in the graft material, due to being constrained bythe aorta or iliac arteries.

Ideally, each strut of each stent segment is secured to the graftmaterial by sutures. In an exemplary embodiment, the suture material isblanket stitched to the stent segments at numerous points to securelyfasten the graft material to the stent segments. As stated above, asecure hold is desirable in preventing relative motion in an environmentin which the graft system experiences dynamic motion arising frompulsatile blood pressure, in addition to pulsation of the arteries thatare in direct mechanical contact with the graft system. The stentsnearest the aortic and iliac ends of the graft system (the uppermostfirst stent segment 310 and the third stent segment 330 respectively)are subject to the pulsatile motion arising from direct internalcontact. These struts in particular should be well secured to the graftmaterial. As illustrated in FIG. 6, the stitches 604 on the upper mostfirst stent segment 310 are positioned along the entire zigzagarrangement of struts. The upper and lower apexes of the third stentsegment may be stitched utilizing a similar configuration. It isdifficult to manipulate the suture thread precisely around the strutsthat are located some distance away from an open end, accordingly,various other simpler stitches may be utilized on these struts, or nostitches may be utilized in these areas.

As illustrated in FIG. 6, each of the struts in the first stent segment310 is secured to the graft material 600 which has been cut to match theshape of the stent segment 310. The blanket stitching 604 completelyencircles the strut and bites into the graft material 600. Preferably,the stitch 604 encircles the strut at approximately five equally spacedlocations. Each of the struts on each end of the third stent segment 330is attached to the graft material, which has been cut to make the shapeof the stent segment 330, in the same manner as the first stent segment310.

A significant portion of the graft will not rest directly againstvascular tissue. This portion of the graft will be within the dilatedaneurysm itself. Therefore, this portion of the graft will notexperience any significant pulsatile motion. For this reason, it is notnecessary to secure the stent segments to the graft material asaggressively as the stent structure described above. Therefore, onlypoint stitches 606 are necessary for securing these stents.

It is important to note that a wide variety of sutures are available. Itis equally important to note that there are a number of alternativemeans for attaching the graft material to the stent, including welding,gluing and chemical bonding.

In accordance with another exemplary embodiment, the present inventionis directed to a device for restraining the cranial end of anendoprosthesis, such as an aneurysmal repair device component, after theremaining portion of the endoprosthesis has been partially or fullydeployed and expands. Some aneurysmal repair system endoprostheses havea bare metal stent portion that extends past the cranial end of thegraft in order to provide some level of supra renal fixation and/oranchoring, see FIG. 1. This stent is in addition to other stents alongthe length of the prosthesis that are generally used to expand the graftmaterial into position. Barbs or hooks are often employed on the suprarenal stent to positively engage the vessel wall as is described indetail herein.

Typically, the endoprosthesis is loaded into a catheter for delivery tothe targeted site. During deployment the endoprosthesis is heldstationary while the outer catheter sheath is retracted and theendoprosthesis expands into position due to the self expandingproperties of the graft material and/or the underlying stent structure.Due to the tortuous nature of the human anatomy, the delivery cathetercomprising the endoprosthesis generally lies up against one side of thevessel prior to deployment. It has been observed in testing that when asupra renal stent with barbs is the first portion of the endoprosthesisto expand, the barbs closest to the vessel wall may make prematurecontact with the wall before the stent has had a chance to fully expand.This creates a situation where the portion of the stent furthest awayfrom the wall during expansion actually accounts for a disproportionateamount of the expansion of the stent in order for the entire stent tomeet the internal diameter of the vessel. The sections of the stent thatare up against the wall do not fully expand and the stent will notachieve full opposition against the vessel wall. Delaying the opening ofthe portion of the supra vessel stent that comprises the barbs allowsthe other portion of the endoprosthesis to move to the centerline of thevessel for expansion and movement of the unexpanded supra renal stentcloser to the center of the vessel lumen. Once this has occurred,subsequent deployment of the supra renal stent with the barbs will notresult in the potential problems described above because every portionof the supra renal stent has the opportunity to expand equally since thebarbs are not close enough to the wall for premature engagement.

In order to accomplish the above, the present invention utilizes anumber of exemplary securing methodologies and associated deliverydevices for restraining the supra renal stent so that it may beselectively deployed after a portion of the rest of the endoprosthesishas been fully or partially deployed and expands.

In accordance with one exemplary embodiment of a stent-graft securementmechanism, both the stent-graft and the delivery device or deliverycatheter are modified. Essentially, the stent-graft securement mechanismcomprises a holding device which is integral with the delivery catheterand an eyelet configuration integral with the distal end of thestent-graft. Each of these components is designed to mate and work withthe other in order to achieve the desired functions; namely, to overcomethe drawbacks associated with currently utilized stent-graft deliverysystems as described above.

Referring now to FIGS. 7 and 8, there is illustrated a section of thedistal end of a stent-graft delivery system in accordance with thepresent invention. FIG. 7 illustrates the delivery system with astent-graft mounted thereon and FIG. 8 illustrates the delivery systemwith no stent-graft. The holding device comprises four basic components,the wire holder 702, the engagement wires 704, the wire guide 706 andthe distal receiver 708. The wire holder 702 is slidably engaged withthe inner member hypotube 700 and functions to hold or secure theengagement wires 704 that pass through the eyelets 802 of thestent-graft 800 as is described in more detail subsequently. The wireholder 702 may comprise any suitable shape or configuration andmaterial. Preferably, the wire holder 702 comprises a substantiallytubular configuration and may be formed from stainless steel orpolycarbonate. A steel wire holder 702 may be fabricated utilizingmachining techniques, while a polycarbonate wire holder 702 may befabricated utilizing moulding techniques. More specifically, the wireholder 702 comprises beveled or angled ends that are designed to notcatch or snag on any other component of the system, including thestent-graft 800 or on the vessel in which the system is deployed. All ofthe beveled or angled ends described herein have the same degree ofangulation. In addition, the wire holder 702 may hold the engagementwires 704 utilizing any suitable means and method. For example, theengagement wires 704 may be held by welding, adhesives, or mechanicalmeans such as tabs 714 on the proximal ends of the engagement wires 704mating with receptacles in the wire holder 702. As illustrated in FIG.7, the engagement wires 704 may run along an outer surface of the wireholder 702, or as illustrated in FIG. 8, the engagement wires 704 mayrun through the wire holder 702 via holes 716. The wire holder 702 alsocomprises a wire release 712 which may be connected to the wire holder702 by any suitable means, such as described herein. In operation, thephysician pulls on the wire release 712 when he or she is ready torelease the distal end of the stent. The wire release runs along thelength of the deliver catheter. A more detailed description of aprocedure is given subsequently.

The engagement wires 704 originate from the wire holder 702 and extenddistally therefrom. The engagement wires 704 pass under the stent-graft800 and pass through the eyelets 802 until they terminate in the distalreceiver 708. The engagement wires 704 may comprise any suitable shapeand configuration. Preferably, the engagement wires 704 comprise asubstantially cylindrical configuration and may be formed from stainlesssteel or a polymer. The wires 704 may be of the same length or ofvarying length. Varying length wires may be particularly useful forutilizing the delivery device for multiple stent-graft deployments. Anynumber of engagement wires 704 may be utilized. Regardless of the numberof engagement wires 704 utilized, it is preferable that the distal endof the stent-graft 800 be held down until full deployment is required bythe medical professional. As stated above, the engagement 704 may runthrough the wire holder 702 (FIG. 8) or along its surface, for examplein grooves (FIG. 7).

The wire guide 706 is fixed to the inner member hypotube 700 distal ofthe wire holder 702. The wire guide 706 may be fixed to the inner memberhypotube 700 in any suitable manner, for example, welding, adhesives orvia a friction or interference fit. The wire guide 706 slidably engagesthe engagement wires 704 in order to retain the axial position of theeyelets 802 when the wire holder 702 is withdrawn proximally. Inaddition, the wire guide 706 may be utilized to capture and secure thedistal or free ends of the engagement wires 704. The wire guide 706 maycomprise any suitable configuration and be formed from any suitablematerial. In a preferred exemplary embodiment, the wire guide 706comprises a substantially tubular configuration and is formed fromstainless steel or polycarbonate. More specifically, the wire guidecomprises beveled or angled ends so as not to catch on any othercomponent. The wire guide 706 comprises a number of openingscorresponding to the number of engagement wires 704 utilized. Theopenings may comprise grooves or through holes. In the preferredembodiment, through holes 718 are utilized as illustrated in detail inFIG. 8. Although it appears as a groove in FIG. 8, the through holes 718are created utilizing an electro-machining technique that first createsa slit opening in the work piece.

It is important to eliminate any potential proximal movement of thestent-graft 800 while the securement mechanism is being withdrawn. Inaddition, it is important to maintain a reduced profile delivery device.Accordingly, the wire guide 706 is designed to solve the movementproblem and the eyelet 802 design, as described in detail below, isdesigned to solve the profile problem. The wire guide 706 is fixed inposition, but allows the engagement wires 704 to slide smoothly throughit in an axial direction. The wire guide 706 also provides the radialretention force on the engagement wires 704 to prevent the eyelets 802from opening outwards until the engagement wires 704 are fully withdrawnfrom the wire guide 706. The geometry of the wire guide 706, bevel ortaper, of the wire guide 706 prevents proximal movement of the eyelets802 due to frictional or bending forces while the engagement wires 704are being withdrawn, thereby improving deployment accuracy. In addition,the wire guide 706 serves or functions as a housing for the ends of theretracted engagement wires 704, thereby minimizing any potentialproblems that may be caused by the ends of the engagement wires 704interacting with the vessel or stent-graft 800.

The distal receiver 708 is fixed to the inner member hypotube 700. Thedistal receiver 708 comprises a number of openings 710 corresponding tothe number of engagement wires 704. Prior to stent release, the distalends of the engagement wires 704 extend into the openings in the distalreceiver 708 where they remain secured. The openings 710 are sized forease of insertion and ease of removal of the engagement wires 704 whilestill providing adequate securement of the engagement wires. The distalreceiver 708 comprises a diameter larger than the diameter of the innermember hypo tube 700, thereby creating an annular space for theengagement wires 704. The distal receiver 708 may comprise any suitableconfiguration and be formed from any suitable material. In a preferredexemplary embodiment, the distal receiver 708 comprises a substantiallytubular configuration and is formed from stainless steel or a polymer.More specifically, the distal receiver 708 comprises a beveled or angledend on the end with the openings 10. The distal receiver 708 may befixed to the inner member hypotube 700 by any suitable means. Forexample, the distal receiver 708 may be fixed to the inner memberhypotube through any suitable means, for example, welding, adhesives orvia a friction or interference fit.

Referring now to FIGS. 9 through 11, there is illustrated a detailedillustration of a single eyelet 802 of the stent-graft 800 as well asother details of the stent-graft securement mechanism. The eyelets 802extend from the apexes 804 of the stent-graft 800 and angle inwardly asdescribed above. Opposite from the eyelets 802 are the engagement barbs806 that secure the expanded stent-graft 800 to the vessel wall. Theeyelet 802 may be an additional element attached to the stent-graft 800,or more preferably the eyelet 802 is integral with the stent-graft 800.In other words, the eyelet 802 is simply a feature of the stent-graft800 cut from the tube that the stent-graft 800 is cut from as describedabove. The eyelets 802 extend from the apexes 804 via protrusions 808.As above with respect to the eyelets 802, the protrusions 808 are cutfrom the same tube. Each eyelet 802 is configured or designed to have anarrow geometry which enables the stent-graft to be crimped whileallowing sufficient room for the engagement wires to pass under thestent-graft 800 and through the eyelets 802. The unique configuration ofthe eyelet 802 that enables this is the tapered and angledconfiguration. As illustrated in the Figures, the eyelet 802 is angledaxially inward toward the center of the stent-graft 800. The angle ofthe eyelet 802 relative to the stent 800 is substantially equal to thatof beveled or angled ends of the wire guide 706. Each eyelet 802 alsocomprises a tapered structure forming a substantially triangularconfiguration. These two features allow the engagement wires 704 toeasily pass through the eyelets 802 as well as provide a reduced profilefor delivery. The tightly nested surfaces also minimize axial movementof the stent-graft 800 when the engagement wires 704 are engaged.

It is important to note that the eyelets 802 may formed from sutures andattached to the stent-graft 800. Alternatively, sutures may be utilizedto augment the eyelets 802.

Recalling that it is desired to maintain a reduced profile and reduceunnecessary movement, the eyelets 802 have a substantially triangular orarrowhead configuration that allows the stent-graft 800 to be compressedwithout strut overlap. In addition, mating the angle of the eyelet 802to the wire guide 706 allows for a secure nesting of the stent-graft tothe delivery system.

In operation, the medical professional positions the stent-graft 800 inthe desired location and retracts the outer sheath thereby exposing thestent-graft and allowing a portion of it to expand. Once this operationis complete, the medical professional may retract the wire holder 702via the wire release 712. The wire release 712 is simply a wireconnected to the wire holder 702 and which runs along the length of thedelivery system to a point where the physician has easy access, such asproximate the handle of the delivery system. This operation allows thedistal end of the stent-graft 800 to expand as illustrated in FIG. 12.

FIG. 11 illustrates the engagement wires 704 retracted from the distalreceiver 708. To complete the procedure, the physician simply continuesto pull the wire release 712 proximally, thereby further retracting thewire holder 702 and freeing the eyelets 802 from the engagement wires.Preferably, the physician will retract the engagement wires 704 into thewire guide 706 so that no free ends of the engagement wires are exposed.The delivery device typically comprises a proximal stop 720 (FIG. 8).Accordingly, the proximal stop 720 may be utilized to ensure that thefree ends of the wires 704 are retracted fully into the wire guide 706by acting as a stop for the wire holder 702.

Although shown and described is what is believed to be the mostpractical and preferred embodiments, it is apparent that departures fromspecific designs and methods described and shown will suggest themselvesto those skilled in the art and may be used without departing from thespirit and scope of the invention. The present invention is notrestricted to the particular constructions described and illustrated,but should be constructed to cohere with all modifications that may fallwithin the scope for the appended claims.

What is claimed is:
 1. A combination of a catheter based stent-graftdelivery system and a stent-graft, the combination comprising: a holdingdevice which is integral with the catheter based stent-graft deliverysystem, the holding device including a wire holder slidably engaged toan inner member of the catheter based stent-graft delivery system,engagement wires, a wire guide having an inner diameter and fixedlymounted to the inner member of the catheter based stent-graft deliverysystem distal to the wire holder, and a distal receiver fixedly mountedto the inner member of the catheter based stent-graft delivery systemdistal from the wire guide; a stent-graft; eyelets integral with thestent-graft and extending from the end thereof, the engagement wiresoriginating from the wire holder and passing through the wire guide andthe eyelets and terminating in free ends in the distal receiver, thewire holder being configured to slide proximally on the inner member,thereby retracting the engagement wires from the distal receiver andeyelets and into the wire guide; wherein the inner member has a distalend and a proximal end and the wire holder has a distal end and aproximal end, and the distal end of the wire holder is substantiallycloser to the distal end of the inner member than the proximal end ofthe inner member; and a collar having an outer diameter and a distal endand a proximal end, the collar coaxially and fixedly mounted on theinner member proximal to the proximal end of the wire holder such thatthe distal end of the collar is substantially closer to the distal endof the inner member than the proximal end of the inner member, whereinthe outer diameter of the collar is greater than the inner diameter ofthe wire holder, such that the collar can stop the proximal motion ofthe wire holder on the inner member.
 2. The combination according toclaim 1, further comprising a wire release connected to the wire holderand extending proximally therefrom.
 3. The combination according toclaim 2, wherein the eyelets are configured as substantially triangularstructures angled radially inward.
 4. The combination according to claim2, wherein when the proximal end of the wire holder is in contact withthe distal end of the collar, the free ends of the engagement wires arein the wire guide.
 5. The combination according to claim 1, wherein whenthe proximal end of the wire holder is in contact with the distal end ofthe collar, the free ends of the engagement wires are in the wire guide.